I know that it uses the VNC protocol to do it's bidding...is there a way to connect to other VNC servers using it's admin interface as a client?
Yes. In Finder, use Command-K (or use the Go->Connect to Server...) menu command, and type
as the connection string. You will be prompted for a password, if necessary.
Remote Desktop will connect to other VNC servers (eg. PCs) if you add them to the list. It will display as "Screen Sharing is Available" but can only use the default port (5900) however support for the other Remote Desktop features is a bit more sketchy.
FWIW The built in Screen Sharing application (which the Finder tip by joev will open) in Leopard is a "dumbed" down version of Remote Desktop's VNC viewer.